Not Applicable
Not Applicable
1. Field of the Invention
The present invention relates generally to radio frequency (rf) or microwave rf power amplifiers. More particularly, the present invention pertains to rf power amplifiers in which field-effect devices are connected in series to proportionally divide a dc supply voltage, and in which both apparatus and method are provided for proportionally shifting or selectively switching rf power between/among a plurality of rf outputs and/or a plurality of antennas.
2. Description of the Related Art
Binary-phase-shift-key (BPSK) modulation is a form of digital modulation in which the rf carrier is phase shifted 180 degrees (inverted) as a digital input changes from 0 to 1. A demodulator, that is a part of an rf receiver, demodulates these phase inversions to recover the original digital stream. Commonly, demodulation is accomplished by a Costas Loop.
A common encoder consists of the rf carrier being inserted into an rf input port of a mixer while a digital input is inserted into an input port of a local oscillator. As the digital input into the input port of the local oscillator changes from an above ground voltage (1) to below ground (0), the output of the mixer changes phase from 0 degrees to 180 degrees.
If the input to the local oscillator were to change polarity (0 to 1, or 0) instantaneously, the phase of the rf output would also change polarity instantaneously. This would cause the output rf spectrum to spread to an unacceptable width.
To prevent this spread in the rf output spectrum (spectrum splatter), commonly, the input to the local oscillator port is filtered (usually with a Bessel filter). As a result, the rf output decreases as the voltage to the input port of the local oscillator is decreased, and the rf output decreases to zero when the input to the local oscillator passes through 0.0 volts. Then the rf output increases in amplitude (with inverted phase) as the voltage to the local oscillator input increases to the opposite extreme.
Therefore, as the filtered input passes through 0.0 volts as the polarity changes, the rf output also passes through a zero rf output condition. This creates a problem in that the rf power amplifier section stages of conventional transmitters consists of several stages biased to Class C. In a Class C amplifier, a zero rf input signal causes the amplifier to shut off. If a Class C amplifier were to follow the above-described encoder, it would shut off every time the input data changes state. This turning off and on of the Class C stages would cause the rf output to occupy far more of the frequency spectrum than allowed by federal regulations.
Lautzenhiser et al., in U.S. patent application Ser. No. 10/028,844, filed Dec. 20, 2001, solves the above-mentioned problems with phase-shifting in general, and binary-phase-shift-key (BPSK) modulation in particular, in that the rf output stays relatively constant as the phase shifts. In one embodiment the phase shifts up to 180 degrees generally linear with a variable phase-control voltage, or shifts 180 degrees in response to a filtered BPSK input.
More particularly, the phase shifts from 0 to 90 degrees in response to a phase-control voltage increasing from 0.0 volts dc to 5.0 volts dc during which time the rf output remains substantially constant; and the rf output continues to be relatively constant as the phase shifts from 90 to 180 degrees as the filtered BPSK input increases from 5.0 volts dc to 10.0 volts dc.
To phase shift the rf output to some angles the entire source-voltage is utilized by a selected one of the solid-state amplifying devices, or FETs, and to phase shift the rf output to other phase angles the source-voltage is dividingly shared, in selected proportions, by two adjacent ones of the solid-state amplifying devices.
Since the rf output remains substantially constant during changes in the phase angle, turning off and on of Class C stages following the encoder is avoided, frequency splatter is avoided, and the occupied frequency spectrum of the rf output follows theoretical values more closely.
In the present invention, in Lautzenhiser et al., application Ser. No. 10/028,844 which was filed on Dec. 20, 2001 and which is incorporated herein by reference thereto, and in Lautzenhiser et al., U.S. patent application Ser. No. 10/091,056 which was filed on Mar. 4, 2002 and which is incorporated herein by reference thereto, two or more solid-state amplifying devices, or FETs, are connected in series in a totem-pole arrangement, and dividingly share a dc source-voltage.
While all three of the above-identified patent applications dividingly share a dc source-voltage, they dividingly share the dc source-voltage for different purposes.
U.S. patent application Ser. No. 10/028,844, two or more solid-state devices, or FETs, are series connected, in a totem-pole arrangement, for the purpose of equally sharing a dc source-voltage that is too high for a single solid-state amplifying device, or FET.
In application Ser. No. 10/091,056, rather than dividing the dc source-voltage equally between/among a plurality of FETs, the dc source-voltage is divided in selected proportions between/among the FETs. And the purpose is different. The dc source-voltage is divided in selected proportions for the purpose of selectively shifting the phase of the rf output.
In the present patent application, similarly to application Ser. No. 10/091,056, the dc source-voltage is also divided in selected proportions between/among a plurality of FETs. But the purpose is different. In the present invention, the dc source-voltage is divided in selected proportions for the purpose of shifting any selected percentage of the rf output, or selectively switching the entire rf output, between/among a plurality of rf outputs or antennas.
Finally, in application Ser. No. 10/091,056 gains of the FETs are selectively controlled in a manner that preferably results in progressive, and generally linear, phase shifting in response to a control input. In contrast, in the present invention, gains of the FETs are controlled in response to a control input to shift selected proportions of the total rf output, or switch the total rf output, between/among a plurality of rf outputs in accordance with any selected pattern and rate, and in accordance with any selected time frame.
However, all three inventions share a common problem. Unless proper rf decoupling is achieved, the maximum rf power output is extremely limited and/or reliability and component life are seriously endangered.
More particularly, totem-pole arrangement of solid-state amplifying devices was taught in a paper published in IEEE Transactions on Microwave Theory and Techniques, Volume 46, Number 12, of December 1998, in an article entitled, xe2x80x9cA 44-Ghz High IP3 InP-HBT Amplifier with Practical Current Reuse Biasing.xe2x80x9d As taught in the IEEE article, in totem pole circuits two, or more, solid-state amplifying devices are used in series for dc operation, but they are used in parallel for rf operation, thereby supposedly solving the disparity between source-voltages and working voltages.
However, totem pole, voltage-dividing, or current-sharing circuits, have been used only at low rf powers, as in the above-referenced article wherein the power was in the order of 10.0 milliwatts. At higher rf powers, inadequate rf decoupling has resulted in low power efficiency, oscillation, a decrease in reliability of the circuits, and destruction of the solid-state amplifying devices.
In contrast to the extremely low rf outputs in which the prior art has been able to utilize totem pole circuitry, Lautzenhiser et al., in the aforementioned patent applications, teach apparatus and method for rf decoupling in which the principles thereof may be used to make totem pole circuits that are limited only by power limitations of the solid-state amplifying devices that are used in the totem pole.
In totem pole circuits, problems with rf decoupling are most severe between the solid-state amplifying devices. For instance, when using FETs, rf decoupling is the most critical with regard to a source terminal of any FET that is connected to a drain terminal of a next-lower FET. Capacitors and rf chokes are used for rf decoupling and rf isolating, but selection and design of capacitor decoupling is the most critical.
The next most critical location for rf decoupling is the source terminal of the lower FET when the source terminal of the lower FET is connected to an electrical ground through a resistor, as shown herein. However, if a negative bias voltage is used for the gate of the lower FET, and the source is connected directly to an electrical ground, this source terminal is already rf decoupled.
Other critical rf decoupling problems are those associated with the source-voltage to the drain of the upper FET and bias voltages to the gates of the FETs. The use of properly designed rf chokes are sufficient to provide adequate rf decoupling in these locations.
Unless rf decoupling is provided as taught herein, reduced efficiency will certainly occur, and both instability and destruction of the solid-state amplifying devices are likely. This is true for the totem-pole circuitry taught by Lautzenhiser et al. in application Ser. No. 10/028,844 in which a source-voltage that is excessive for a single solid-state amplifying device is dividingly shared, for phase-shifting rf amplifiers taught by Lautzenhiser et al. in U.S. patent application Ser. No. 10/091,056, and for power-shifting rf amplifiers taught herein.
The present invention provides apparatus and method for selectively proportioning rf power to a plurality of rf outputs or antennas. The method includes splitting a single rf signal into a plurality of split rf signals; separately power amplifying the split rf signals into the plurality of rf power outputs; selectively proportioning gains of the power amplifying steps; and maintaining a summation of the gains substantially constant.
The apparatus and method of the present invention also provides apparatus and means for selectively switching rf power from one rf output, or one antenna, to an other rf output or antenna. Whether selectively proportioning or switching, by maintaining the gains of the amplifying steps substantially constant, the rf power is maintained substantially constant during either the selective proportioning step or the switching step.
Preferably, the method of the present invention includes series connecting a plurality of solid-state current devices, which preferably are FETs, between a dc supply voltage and a lower dc voltage; splitting an rf input signal into the plurality of split rf signals; separately power amplifying the split rf signals in the series-connected solid-state current devices into the plurality of power outputs; selectively proportioning gains of the separate amplifying steps; and maintaining a total rf power substantially constant during the selective proportioning step.
The apparatus and method of the present invention may be used as a solid-state switch for selectively connecting an rf signal to a primary rf power amplifier and a redundant rf power amplifier, thereby providing for continuing rf power when the primary rf power amplifier fails.
The apparatus and method of the present invention may be used to selectively proportion rf power outputs, or to selectively shift rf power outputs, between top and belly-mounted antennas of an airplane, and may be used to selectively proportion rf power, at zero or quadrature phase angles, among antennas in an array.
Depending upon the type of splitters that are used, the selectively proportioned rf outputs may be in-phase or at angles such as 0, 45, 90, and 270 degrees. One preferred type of splitter is a Wilkenson splitter.
Finally, as taught herein, as taught by Lautzenhiser et al. in application Ser. No. 10/091,056, and as taught by Lautzenhiser et al. in application Ser. No. 10/028,844, a mounting technique is provided for FETs that avoids both over heating and the resultant danger of destroying the internal junctions of the solid-state amplifying device, while maintaining electrical isolation from a circuit ground, in circuits wherein the source terminal of a FET is the mounting flange of the packaged FET.
In a first aspect of the present invention, a method for selectively proportioning rf power to a plurality of rf outputs comprises: splitting a single rf signal into a plurality of split rf signals; separately power amplifying the split rf signals into the plurality of rf power outputs; selectively proportioning gains of the power amplifying steps; and maintaining a summation of the gains substantially constant.
In a second aspect of the present invention, a method for selectively proportioning rf power to a plurality of rf outputs comprises: series connecting a plurality of solid-state current devices between a dc supply voltage and a lower dc voltage; splitting an rf input signal into a plurality of split rf signals; separately power amplifying the split rf signals in the series-connected solid-state current devices into a plurality of power outputs; selectively proportioning gains of the separate amplifying steps; and maintaining a total rf power substantially constant during the selective proportioning step.
In a third aspect of the present invention, a method for selectively proportioning rf power to a plurality of antennas on an airplane comprises: splitting a single rf signal into a plurality of split rf signals; separately power amplifying the split rf signals into a plurality of rf power outputs; separately connecting the rf power outputs to respective ones of the antennas; selectively proportioning gains of the power amplifying steps; and maintaining rf power substantially constant during the selectively proportioning step.
In a fourth aspect of the present invention, a method for selectively proportioning rf power among an array of antennas comprises: splitting a single rf signal into a plurality of split rf signals; separately power amplifying the split rf signals into a plurality of rf power outputs; separately connecting the rf power outputs to the antennas; selectively proportioning gains of the power amplifying steps; and maintaining rf power substantially constant during the selectively proportioning step.
In a fifth aspect of the present invention, a method for rf power amplifying comprises: series connecting upper and lower solid-state current devices between a dc supply voltage and a lower dc voltage; separately amplifying rf signals in the solid-state current devices with an rf output of the upper solid-state current device exceeding about 100 milliwatts; and making an rf effective series resistance between the series connection of the solid-state current devices and an electrical ground less than 0.4 divided by the rf output in watts.
In a sixth aspect of the present invention, a method for phase-shifting an rf output comprises: splitting an rf input into first and second rf signals that are at different phase angles; inputting the first rf signal into a first solid-state amplifying device; inputting the second rf signal into a second solid-state amplifying device; amplifying a selected one of the rf signals; and combining the rf signals subsequent to the amplifying step.
In a seventh aspect of the present invention, a method for phase-shifting an rf output comprises: splitting an rf input into first and second rf signals that are at different phase angles; inputting the first rf signal into a first solid-state amplifying device; inputting the second rf signal into a second solid-state amplifying device; proportionally amplifying the rf signals; and combining the rf signals subsequent to the amplifying step.
In an eighth aspect of the present invention, a method for binary-phase-shift-key modulating comprises: splitting an rf output into 0, 90, and 180 degree rf signals; separately amplifying the rf signals; combining the separately amplified rf signals into a single rf output; and preventing the single rf output from decreasing to zero when the rf output is shifted 180 degrees.